Oxidation and esterification of cracked gas oil



OXIDATION AND ESTEREFICATION F CRACKED GAS fill Stanford J. Hetzel, Cheitenham, Pa., assignor to Sun Oil Company, Philadelphia, Pa, a corporation of New Jersey N0 Drawing. Application June 15, 1951, Serial No. 231,897

Claims. (Ci. 260-469) This invention relates to the preparation of valuable materials from cracked gas oil obtained in mineral oil cracking processes.

This application is a continuation-in-part of my three copending applications Serial Nos. 194,013, 194,014, and 194,015, all filed November 3, 1950, all now abandoned.

Cracked gas oil, sometimes referred to as recycle stock, is a product, boiling in the gas oil range, obtained in thermal or catalytic cracking, of Which the products include cracked gasoline and a heavier fraction, cracked gas oil. The starting material to which the present invention is applied is a material boiling through the range 510 F. to 575 F. and comprising the aromatic constituents which are normally present in a cracked gas oil. Within this definition of starting material are included: cracked gas oils as obtained directly from distillation of cracking products, such gas oils having an initial boiling point not substantially higher than 510 F. and a final boiling point not substantially lower than 575 F.; and aromatic concentrates obtained from such cracked'gas oils and having boiling range specifications as specified above. Such aromatic concentrates can be obtained by means known in the art, e. g. by selectively adsorbing the aromatic constituents on silica gel.

Thus, the starting material according to the present invention contains a Wide boiling range mixture of aromatic compounds of the type ordinarily found in cracked gas oil, and may or may not also contain substantial, sometimes major proportions, of nonaromatic constituents, i. e. saturated and olefinic constituents.

The boiling range of the starting material can be much wider than 510 F. to 575 F., but the starting material should contain a substantial proportion of constituents boiling within the 510 F. to 575 F. range, and preferably contains at least 30 percent of such constituents.

Cracked gas oil for use according to the present invention can be a product obtained either from cracking a previously uncracked stock, or from cracking a previously cracked recycle stock. Products obtained from the latter type of cracking operations have generally higher aromatic contents and are therefore somewhat preferred for use according to the present invention.

Cracked gas oil, when used as a recycle stock for further cracking, becomes more refractory to cracking each time it is cracked and eventually becomes so refractory that it is not economical to crack it again. No more satisfactory use than as a fuel has been found previously for refractory gas oils of this type. It is highly desirable to find some means for making more valuable products from such gas oils.

According to the present invention, starting materials comprising cracked gas oils or aromatic concentrates therefrom are contacted with dilute nitric acid at elevated temperature to obtain saponifiable reaction products. It has been found that large yields can be obtained of mixtures of saponifiable materials, which mixtures are capable of esterifying low molecular weight alkyl alcohols to form Wide boiling range mixtures of esters which are, despite 2,76,272 Patented Oct. 9, 1956 their wide boiling range, highly satisfactory plasticizers for vinyl polymers.

According to the invention it is for several reasons preferred to use as starting material a cracked gas oil without previously removing nonaromatic constituents therefrom. First, it has been found that the nonaromatic constituents do not interfere with the formation of saponifiable materials, so that the expense of removing them can be spared. Furthermore, the yields of saponifiable materials are generally substantially higher when the preferred starting material is used indicating probably that some proportion of the nonaromatic constituents reacts to form saponifiable materials. Furthermore, the reaction products obtained are considerably more fluid, and therefore easier to handle in commercial apparatus when the preferred starting material is used.

In contacting hydrocarbon starting materials with nitric acid according to the invention, it is preferred that the concentration of the nitric acid not exceed 40 percent, in order that nitration be avoided. The concentration is preferably at least about 10 percent. Some variation from these concentration limits can be used in particular instances. The concentration of the nitric acid generally declines during the course of the reaction, and it is some times desirable to add nitric acid to counteract this tendency.

The relative amounts of nitric acid and of hydrocarbon material which are contacted according to the invention can vary. Preferably, the total amount of HNOs used per mole of aromatic hydrocarbon is at least about 2 moles, i. e. about 126 weight units. The mole ratio of HNO; to hydrocarbon material is preferably 2-8, more preferably 3-5. Preferred operation is to contact hydrocarbon material initially with one portion of the nitric acid and to add the rest subsequently during the course of the reaction, the total amount of nitric acid used preferably being as specified above.

The temperature at which the nitric acid and hydrocarbon material are contacted is preferably within the approximate range 160 F. to 250 F. If the contacting is performed at atmospheric pressure, the temperature is more preferably in the neighborhood of the boiling point of the aqueous phase. If higher temperatures are used, the contacting is performed at elevated pressure, e. g. up to about pounds per square inch.

A preferred manner of operation is to pass vapors evolved from the reaction mixture upwardly countercurrent to descending nitric acid in a condensing zone in order to dissolve the vapors in the nitric acid, and then introduce the nitric acid into the reaction mixture. This is a preferred manner of adding nitric acid during the course of the reaction. In this manner, evolved nitrogen oxides are recovered for re-use, and the concentration of the nitric acid in the reaction zone is maintained at a suitable level.

The length of time for which the reaction is continued varies according to the reaction conditions employed and to the yield of saponifiable materials desired. When using the preferred conditions specified above, a saponifiable material yield of almost 50 weight percent, based on the weight of the aromatic constituents of the hydrocarbon charge material, can be obtained in 10 hours. With longer reaction times, yields of weight percent or greater can be obtained.

Catalysts can be used in the reaction, e. g. manganese dioxide, vanadium oxide, ammonium vanadate, or other suitable catalyst. Fresh oxygen can be supplied to the contacting zone during the course of the reaction, if desired.

The reaction products obtained according to the invention generally comprise three layers: an upper oil layer, mostly unreacted hydrocarbon; an intermediate aqueous layer; and a lower tarry layer, mostly saponifiable material. The tarry layer is generally a caked solid when aromatic concentrates from cracked gas oil are used as starting materials, and is generally a liquid layer when cracked gas oil itself without removal of nonaromatics is used as starting material. In some instances, particularly with relatively long reaction times, the aqueous layer contains in suspension substantial quantities of crystalline solid material, which probably comprises carboxylic acid.

The valuable saponifiable materials produced by the reaction are mostly in the tarry layer, but are also contained in the upper oil layer to a small degree. The upper oil layer and the tarry layer can be separated from the aqueous layer, and the saponifiablematerials in either the oil or the tarry layer or both can be deoiled, either together or separately. Alternatively the upper oil layer or the tarry oil layer or both, either together or separately. can be esterified, and a wide boiling range mixture of esters separated from the crude esterification products. it is preferred, however, to deoil the saponifiable materials before esterification, since in this way vaporization of large quantities of hydrocarbon from the crude esterification products is rendered unnecessary.

Saponifiable materials can if desired be recovered from the yellow crystalline solids, if any such solids appear in the aqueous phase.

Deoiling of the saponifiable material can be accomplished by saponifying the upper oil layer or the tarry oil layer or both, either together or separately, and contacting the saponified product with a selective solvent for hydrocarbon, e. g. diethyl ether, petroleum ether, etc. The aqueous layer remaining after such extraction can then be acidified whereupon a sludge compriisng the desired saponifiable material is precipitated. The sludge is sepa rated from the aqueous phase and further purified if desired. In any event, the product obtained is a valuable mixture of saponifiable materials obtained from a wide boiling range starting material.

The product obtained is generally a black vicous liquid or black low-melting solid. When aromatic concentrates from cracked gas oil are used as starting materials, the product is generally a low melting solid at ordinary temperatures. When cracked gas oil itself is used, the product is generally a viscous liquid at ordinary temperatures.

The chemical constitution of the product obtained is unknown. The action of nitric acid on various hydrocarbons is sufliciently complex that the product can probably be assumed to be a complex mixture. Since cracked gas oils generally contain substantial quantities of alkylated naphthalenes, it is possible that the product contains naphthoic acid and alkyl naphthoic acids in some proportion, but the invention is not to be limited by any theory.

The product obtained can be esterified with an alkyl alcohol having 1 to 8 carbon atoms. The method of esterification employed can be any suitable known method, for example, the esterification can be accomplished by refluxing together approximately one mole of the alcohol with 200 grams of the mixture of acidic materials in the presence of a solvent and a catalyst if desired. An excess of the alcohol can be used, the excess acting as a thermostatic solvent. The desired product can be obtained from the esterification reaction products, for example, by vacuum distilling the products to obtain a fraction higher boiling than any of the components of the original reaction mixture. This fraction comprises a wide boiling range mixture of esters. Alcohols which can be used in the esterification include methyl and ethyl alcohol and propyl, butyl, amyl, hexyl, heptyl, and octyl alcohols, either straight chain or branched chain. The alcohols may be substituted with noninterfering substituents. As stated above, the esterification can be conducted in the presence of unreacted hydrocarbon materials, in which case the hydrocarbons can be distilled from the esterification products, and the ester product mentioned above can then be distilled as a heavier fraction.

Esterifications performed as described give remarkably high yields of materials suitable for plasticizing vinyl polymers. Although the acidic materials used in the esterification are most likely highly complex, they are apparently free from materials which would substantially interfere in the esterification or in plasticizing of vinyl polymers.

The wide boiling range mixtures of esters obtained as described above have been found to be highly satisfactory plasticizers for vinyl polymers.

Vinyl polymers, as contemplated herein, include homopolymers, copolymers, or interpolymers of vinyl monomers, i. e. monomers containing a vinyl group, CH2=C in the molecule. Examples of vinyl monomers include styrene, substituted styrenes, vinyl naphthalene, acrylic acids, acrylic acid esters .such as methyl acrylate and methyl methacrylate, vinylidene halides, vinyl halides, acrylonitrile, vinyl acetate, vinyl benzoate, vinyl caproatc, divinyl succinate, vinyl acrylate, vinyl ethyl ether, vinyl butyl ketone, etc. Other vinyl polymers can be plasticized by the esters of the present invention, such as the resins obtained as a result of reaction between polyvinyl alcohol and aldehydes. Polyvinyl formal, polyvinyl acetal, and polyvinyl butyral resins are illustrative of the later group of resins.

The esters contemplated by the present invention can be used as vinyl polymer plasticizers either alone or in combination with known plasticizers, such as dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, and the like.

The proportion of ester to polymer in compositions according to the present invention can vary; in most cases, 20 to 150 parts by weight of ester per 100 parts of polymer are suitable proportions. Preferred proportions are 40 to parts by weight of ester per parts of polymer.

The ester mixture can be incorporated with the vinyl polymer in any suitable maner, e. g. by milling, molding, dissolving together in solvents, etc.

The following examples illustrate the invention:

Example I In this example, an aromatic concentrate from a catalytically cracked gas oil was contacted with dilute nitric acid according to the invention. The cracked gas oil was a second pass" catalytic gas oil obtained by cracking recycle stock. The aromatic concentrate was prepared by percolating the gas oil through a bed of slica gel, and recovering the adsorbed aromatic constituents by the use of a desorbing agent according to a method known in the art.

The catalytic gas oil prior to removal of nonaromatic constituents had a boiling range of about 480 F. to about 600 F. and had the following approximate proportions:

400 grams of the aromatic concentrate were admixed with nitric acid (10 percent concentration) and the resulting mixture was heated for 94 hours at about 212 F. under refluxing conditions. The total amount of 10% nitric acid used during the 94 hour period was eight liters. At the end of the 94 hour period, the reaction products were cooled whereupon three main phases appeared in the products: an upper oil layer; an intermediate aqueous layer containing yellow crystalline solids in suspension;

and a, dark solid cake on the bottom of the reaction zone.

The two upper layers were decanted, and the remaining cake Was saponified with caustic soda. Unsaponifiable material was removed from the saponified products by extraction with diethyl ether to obtain an aqueous rafiinate containing soaps of the desired acidic product. The raffinate was acidified with hydrochloric acid and extracted with diethyl ether. The extract from the second ether extraction was washed with water and distilled to remove ether and leave as residue 357 grams of a black lowmelting solid constituting the desired mixture of saponifiable materials. Assuming an average molecular weight of 180 for the charge material, and assuming a monocarboxylated product, the mole percent yield of saponifiable materials in the product mixture was about 77 percent. This does not represent the total yield of saponifiable materials, since 116 grams of yellow crystalline solids were recovered by filtration of the aqueous layer of the reaction products, and these solids were found to contain substantial proportions of saponifiable materials.

This example shows that high yields of saponifiable materials can be obtained from aromatic concentrates from cracked gas oils by contact with nitric acid accord ing to the present invention.

Example II In this example, the same gas oil as in Example I was contacted with nitric acid without previous removal of nonaromatic constituents. 200 grams of the gas oil were admixed with percent nitric acid and the resulting mixture was heated for 75 hours at about 212 F. under refluxing conditions. The total amount of 10 percent nitric acid used was four liters. Upon cooling the reaction product, three main phases appeared: an upper layer, an intermediate aqueous layer containing yellow crystalline solids in suspension, and a lower, liquid, tarry oil layer. The entire reaction product was filtered to remove the crystalline solids. Saponifiable materials were recovered from the filtrate by the saponification, extraction, and acidification procedure described in Example I. The saponifiable product mixture obtained weighed 80 grams and was a black, very viscous liquid. The mole percent yield based on the aromatics in the charge material, was about 85 percent, exclusive of the yellow crystalline solids, of which 18 grams were obtained.

This example shows that the yield of saponifiable material can be greater when cracked gas oil is treated according to the present invention without previous removal of non-aromatics than when an aromatic concentrate from cracked gas oil is treated.

Example III In this example, a first pass catalytic gas oil obtained by cracking a previously uncracked stock, was contacted with dilute nitric acid, without previous removal of nonaromatic constituents. The gas oil had a boiling range of about 420 F. to about 670 F. and contained about 36 percent aromatic hydrocarbons. The relative proportions of the various types of aromatic hydrocarbons were about the same as in the gas oil treated in Example II. The contacting conditions were essentially the same as those employed in Example II except that the quantities of materials, though used in the same proportions, were twice as great. The mole percent yield of the saponifiable materials recovered from the filtrate was about 90 percent. In addition 43 grams of yellow crystalline solids were obtained.

This example shows that high yields of saponifiable materials can be obtained from first pass cracked gas oil as well as from second pass cracked gas oils.

Example IV In this example, a wide boiling range ester mixture was prepared according to the invention. The alcohol used was n-bu-tyl alcohol. The acidic material used was a black low-melting solid material prepared, in a manner similar to that described in Example I, from an aromatic concentrate from second pass catalytic gas oil. 84 grams of the acidic material were refluxed with cc. of n-butyl alcohol for 10 hours in the presence of 5 cc. of concentrated sulfuric acid as catalyst. At the end of the 10 hour period, the reaction products obtained were vacuum distilled to obtain as esterification product, a fraction boiling between C. and 240 C. at 2 mm. Hg and weighing 42.5 grams. 40.5 grams of residue were obtained from the distillation.

Example V In this example, a wide boiling range mixture of 2-ethyl hexyl alcohol esters was prepared according to the invention from an acidic material obtained, in a manner similar to that described in Example I, from an aromatic concentrate from second pass catalytic gas oil. 100 grams of the mixture of acidic materials were refluxed together with 75 grams of 2-ethyl hexanol for 10 hours in the presence of 250 cc. of xylene and 5 grams of paratoluene sulfonic acid. Water from the esterification was removed continuously in a Dean-Stark tube. At the end of the 10 hour period, the reaction products obtained were distilled and a fraction boiling between 172 C. and 275 C. at 2-3 mm. Hg was taken as the desired product.

Example VI In this example, a composition comprising polyvinyl chloride plasticized with a wide boiling range mixture of esters of n-butyl alcohol was prepared. The mixture of esters was that prepared as described in Example IV. 76 parts by weight of a polyvinyl chloride resin known commercially as Geon 101 were mixed together with about 1.2 parts by weight of lead carbonate and about 0.6 parts by weight of stearic acid in the dry state by ball milling. About 52 parts by weight of the mixture of esters were added in a cake mixer and the mass stirred thoroughly until good mixing was obtained. This mass was then fused on a 3" x 8" rubber mill whose rolls were heated to a temperature of about 285 F. The banded material was cut several times from each side and sheeted off to give a homogenous plastic sheet comprising polyvinyl chloride plasticized with the esterification product. The sheet had good appearance, odor, flexibility, strength, and drape, and no tendency for exudation of plasticizer was observed.

This example shows that the n-butyl ester of a mixture of acidic materials obtained by nitric acid oxidation of second-pass catalytic gas oil aromatics is a good plasticizer for polyvinyl chloride resin.

Example VII In this example, a composition comprising polyvinyl chloride plasticized with a wide boiling range mixture of esters of 2-ethyl hexanol was prepared. The mixture of esters was similar to that prepared as described in Example V. 52 parts by weight of the mixture of esters were fused together with 76 parts of Geon 101 in a manner similar to that described in Example VI. The plastic sheet obtained had good appearance, odor, flexibility, strength, and drape, and no tendency for exudation of. plasticizer from the sheet was observed.

This example shows that 2-ethylhexyl esters as well as n-butyl esters, of acidic materials as herein contemplated are good plasticizers for polyvinyl chloride resin.

Substantially similar results are obtained when the esters as herein contemplated are used to plasticize other vinyltype polymers, such as polyvinyl acetal, polymers of styrene, meth'l methacrylate, vinylidene chloride, acrylonitrile, vinyl acetate, 'divinyl adipate, vinyl ethyl ether etc.

The invention claimed is:

1. As a new composition of matter, acidic materials prepared by contacting with dilute nitric acid at elevated temperature a petroleum hydrocarbon material, boiling through the range 510 F. to 575 F., selected from the 7 group consisting of cracked gas oil and aromatic fractions separated from cracked gas oil.

2. As new composition of matter, esters of an alkyl alcohol having 1 to 8 carbon atoms with acidic materials prepared by contacting with dilute nitric acid at elevated temperature a petroleum hydrocarbon material, boiling through the range 510 F. to 575 F., selected from the group consisting of cracked gas oil and aromatic fractions separated from cracked gas oil.

3. Composition according to claim 1 wherein said petroleum hydrocarbon material is cracked gas oil.

4. Composition according to claim 1 wherein said petroleum hydrocarbon material is an aromatic fraction separated from cracked gas oil.

5. Composition according to claim 1 wherein said acidic materials have been separated from unsaponifiable materials contained in the products of said contacting.

6. Composition according to claim 2 wherein said petroleum hydrocarbon material is cracked gas oil.

7. Composition according to claim 2 wherein said petroleum hydrocarbon material is an aromatic fraction separated from cracked gas oil.

8. Composition according to claim 2 wherein said esters are prepared from acidic material which has been separated from unsaponifiable materials contained in the products of said contacting.

9. A composition of matter comprising esters of a butyl alcohol with a mixture of acidic materials prepared by contacting with dilute nitric acid at reactive temperature an aromatic fraction separated from cracked petroleum gas oil, said aromatic fraction boiling through the range from 510 F. to 575 F., said esters boiling mainly within and through the range from 160 C. to 240 C. at 2 mm. of Hg.

10. A composition of matter comprising esters of an octyl alcohol with a mixture of acidic materials prepared by contacting with nitric acid at reactive temperature an aromatic fraction separated from cracked petroleum gas oil, said aromatic fraction boiling through the range from 510 F. to 575 F., said esters boiling mainly within and through the rangefrom 172 C. to 275 C. at 2-3 mm. of Hg.

References Cited in the file of this patent UNITED STATES PATENTS 1,866,632 Drescher et al. July 12, 1932 2,054,100 Scott et a1. Sept. 15, 1936 2,157,697 Hagedorn May 9, 1939 2,250,204- Iuettner July 22, 1941 2,298,670 Alleman Oct. 13, 1942 2,331,328 Kyrides Oct. 12, 1943 2,438,753 Kellog Mar. 30, 1948 2,443,093 Bruun et al June 8, 1948 FOREIGN PATENTS 301,079 Germany Aug. 3, 1916 

1. AS A NEW COMPOSITION OF MATTER, ACIDIC MATERIALS PREPARED BY CONTACTING WITH DILUTE NITRIC ACID AT ELEVATED TEMPERATURE A PETROLEUM HYDROCARBON MATERIAL, BOILING THROUGH THE RANGE 510* F. TO 575* F., SELECTED FROM THE GROUP CONSISTING OF CRACKED GAS OIL AND AROMATIC FRACTIONS SEPARATED FROM CRACKED GAS OIL. 